Adventure time:worlds in danger
by jackthehedghog
Summary: First fic with Normal At and Gender Bent At crossing worlds. With the help of a mysterious new assassin he meets at the bar, It seems as though Ice king's dream of meeting Fionna and cake is actually going to come true. but... is the price he has to pay, really worth it? Rated M for Blood, gore, and future scenes i can not describe in this summary


Adventure time: Trouble between Ooo and Aaa.

**Hey everyone, yeah I know I really shouldn't be starting another fanfiction, but screw it I just had to do a crossover fanfic of Ooo and Aaa. Though to be honest some of the inspiration came from Insanity, or madman, can't really tell who's who most of the time, anyway there adventure time FIc's are great and really worth checking out.**

**Ok, enough Advertising… Let's get down to what's to be expected here. As the title suggests, this is a crossover of the original and gender bent world of adventure time. and it is already known that both side's will meet, but this time they won't immediately be friends, and it won't be so easy for the two sides to develop a relationship.**

**Furthermore, this story takes place after Flame princess reclaimed her throne and now has cinnamon bun by her side. I don't mean in a romantic kind of way, Cinnamon bun just has great respect for Fp. **

**It was obvious that Finn needed to reflect on thinks and learn not to be such a needy pussy. I know that's a bit too far, but Finn was acting out of line that time. …**

**Anyway, even though He's had his friends to help him get back to his old self, it's been moving at a slow pace…**

**And some of my At Oc's will appear in here so there's that…**

_Chapter 1: A princess without a heart?_

Our story begins with Ice king, oddly enough. He was flying across a long path between two mountains. It had seemed as though he was flying straight towards a dead end. But he had said the magic words before coming in contact with the walls.

"Wizards rule." Ice king spoke. The walls had disappeared revealing a large city. As soon as he flew above the streets, the walls behind him had reappeared blocking visions of the city.

Down below wizards were just doing their normal wiz biz as usual. Fake wizards got sniped but the po po of the city, and real wizards usually battled amongst each other.

"Ok, if that little tip the cutie gave me is right, then I should find my guy at the place where all the magical peeps with broken dreams hang out.

After a few minutes of flying, ice king had finally came to a lit up tavern in a dark alleyway.

There seemed to be a lot of hooping and whooping and smashing going on from inside.

"Here it is, the broken staff, this must be the place." Ice king had entered the tavern. But as soon as he did, a half empty flask of happy elixir came flying towards the cold king's head.

"Oh jeez!" ice king quickly ducked letting the glass break against the wall. He may have been old but he had good reflexes, for an old timer anyway.

When he had looked up again he had saw someone who was wearing a dark brown hood over his head with a large button up trench coat with black baggy jeans and brown loafers.

Under the clock he was wearing a sleeveless red and white shirt with white straps. At the moment he has seemed to be drunk of his patoot.

"HEY! Bartender! 5 MORE ROUNDS OF MAGIC ELIXER OVER HERE!" the youth had yelled at the top of his lungs.

"Coming right up pal." The bartender replied with a disappointed look on his face. the youth under the hood was no younger then about 16 years of age, and yet here he was drinking himself stupid.

"Seems young, wearing weird garbs, loves to drink magic elixir, this seems like the guy, but he sounded a lot more dark and depressing from the description. Oh well, beggar's can't be chooser's." Ice king shrugged.

As he began to approach the table the youth was dancing upon, it seemed like someone else already had a bone to pick with the hooded boy.

To ice king's surprise it was huntress wizard, and she did not look happy.

"Hey, are you the turd that's posing as an assassin?" Huntress wizard snarled already getting the youth's attention.

"Huuuuuuuuhhh? Are you talking to (burp) me?" the hooded youth questioned with a slurred tone.

Already huntress wizard was getting steamed because he was acting like he didn't even know what he did.

"YES YOU! aren't you the guy who stole my mark! That bounty could have set me for life it wasn't for you!" Huntress wizard growled. But much to her displeasure, the hooded youth only laughed drunkily once again.

"What?! I don't remember there being a rule where you could call on marks, I thought it was always first come first kill?" The youth asked goofily placing a palm over his face.

At this point huntress wizard was about ready to ring someone's neck.

The youth managed to regain some stability and had crouched on the counter so he could meet huntress Face to dace.

"Listen, many apologies of preventing you from advancing your own carrer, but you can't expect to always be the one to get a high price bounty, how about the next time were hunting the same bounty, if you have the victim's neck in your hands it's your kill, but until then, I suggest you be the bigger man here and just enjoy a swig. On me." The youth spoke goofily.

But huntress wizard had only slapped the flask out of the youth's hand.

"Well, that wasn't very nice." The youth frowned at the broken flask and spilled elixir.

"Next time I see you, I'll destroy you!" Huntress growled clenching the youth's neck collar.

"Hey does anyone have a nickel?" the youth grinned.

Huntress wizard was at a lose and just decided to walk away.

She had shoved ice king out of the way and stormed towards the exit of the tavern. "Out of the way frosty." Huntress wizards snarled.

"Yoinks, someone's had there buttons pressed." Ice king said as he turned around to look at the youth who was still guzzling down glass after glass of magic elixir at the nearby table.

He had decided to take a seat next to the drunken youth who could be clarified as an assassin, judging from the argument with huntress wizard a few minutes earlier.

"Uh hi there, you wouldn't happen to be Jak? Jak brawler?" Ice king asked.

The youth had sharply turned around to the ice king with a dark serious expression on his face scaring the ice king for a split second.

"Uh, a-are you him?" Ice king asked worriedly.

"YEP! That's a me, Jak Brawler, the name that has even less worth then this glass!" Jak smiled as he had smashed another clash on the counter top.

The king of ice was a bit surprised at the quick change of attitude from jak, maybe he was bi polar or something?

"SO, (burp) what brings you to one of the only bars in this forsaken land that'll serve someone a glass Of M.E.?"( Magic elixir) jack asked as he had signaled the bartender to bring him another glass.

"Well, a beautiful girl told me you were the guy I would need to go to if I wanted a job done, says you're a class act assassin." Ice king explained. But jack had only sighed.

"Believe me old man, I'm far from any class act you'll find in ooh, anyway if your looking for assasin's why didn't you ask the chick that just stormed out of here?" Jak questioned refereeing too huntress wizard.

"Well she's got some skill but I heard she's still starting out as an assassin, but you have a special skill that I need, I forget what my friend called it, a guide bearer or something?" ice king pondered.

But upon hearing that word, jack had quickly slammed his glass on the countertop, it didn't break, but jack wasn't feeling very cheerful at the moment.

"Where did you get that information old man?!" Jack questioned with a hint of hostility in his voice.

"W-what's wrong man? I thought we were cool?" Ice king asked backing up a little bit.

"Listen, as long as you have the money I'll find the person, but I don't want you saying that word again or else your head's going to be roasting over a fire place."

"(Gulp), n-no problem man, no worries man, I haven't even heard of the word gu-" ice king stopped himself as jack had gave a serious glare at him before he could even finish.

"Uh, you know what, I didn't say anything, nothing at all." Ice king laughed nervously .

Jak had only averted his glare and turned back to his drink. "So what's this thing you need me to do anyway?"

"Well, this plan is going to be a real dozy, you see." As ice king had began explaining the job he wanted the assassin to do, the champion of ooh were busy with other matters.

_It was storming over the tree house, knives raining everywhere and water surrounding the tree house._

_Everything was dark and nothing could be seen except a blowtorch moving across the unusually long corridors of the tree house. The only thing that could be heard were the thunder crashes in the storm and the sound of boots against the wooden planks._

_The torch had revealed it was Finn who was walking along the halls. He was wearing a candy cane striped shirt with a large baby blue style trench coat with a long black belt along with a rapier in a sheath along with longer blue pants then usual with black boots and a black colored version of his normal hat._

_He had walked through the door and had came to a rickety, moss filled bridge. The bridge look unsafe to walk across, but what was on the other side of the bridge made Finn push on._

_On the other side of the door was a orange jeweled, locked door._

"That must be it, that old sea serpent's treasure room, time to get what's rightfully mine and abandon ship." Finn spoke to himself as he had began walking across the bridge.

Unknown to him, a small oval shaped shadow was following right behind him.

In only a few minutes Finn had made it across the bridge. When he got to the door, he had reached into his left coat pocket grabbing a orange skull key and putting it in to the lock.

As soon as the door unlocked, Finn had walked through and had found a old chest. When he opened it, a look of satisfaction appeared on the hero's face as he had found what he was looking for.

"There you are, now that I have my possessions, it's time i…" Finn was cut off as he had heard someone enter the room.

"And just where do you think your going with my treasure boy?" the voice questioned in what sounded like a horrible pirate voice.

"Finn had turned around to see His best friend and brother Jake who was using his stretchy powers to wear a captain's outfit of his own design.

"I do hope you didn't plan on leaving this vessel without the permission of the captain." Jake chuckled as Finn had slammed the chest closed and turned to him.

"Well if it isn't butt beard the pirate, you knew all along didn't you?" Finn questioned clenching his fist.

"Aye, that I did Mr. Blue blood, I knew you were searching for whatever remained of that family sword, you became to attached to it, it was only a matter of time before you were going to find it then leave without even a goodbye." Butt beard said already reaching for his weapon.

"So you understand that I'm going to leave this ship and go back to my island right?" Blue blood asked folding his arms.

But orange beard had laughed only louder at the boy.

"I don't think you'll be leaving boy, you still have so much to offer to this ship and it's crew, especially the young dame aboard."

"Can it butt beard, I told you once that I was over her!" Blue blood(Finn) had snapped.

"Are you now? judging by the way you act at the mention of her, I would beg to differ." Butt beard (Jake) chuckled.

"Tch" Finn had bit his tongue and had turned away from butt beard not wanting to admit he still had thoughts about her.

"Weather you still have feelings for the wee lass or not, I'm afraid you don't have too many options here blue blood, you could either stay here on this vessel and we can forget this little incident ever occurred. Or….

Butt beard began as he had turned his left arm into knife like weapon.

You could chose to defy me, which ends with your neck meeting the edge of my cutlass."

Finn had glared at butt beard wondering if abandoning ship was such a wise idea.

"So what do you say lad? Will ye stay on the ship?" Butt beared asked politely holding out his hand for a hand shake.

But depite the situation, Blue blood was intent on escaping.

"I'd sooner walk the plank and dance with the sharks then being a member of your crank shaft crew another second." Blue blood replied.

Butt beard had sighed at his decision.

"Believe me boy, that can be arranged sooner then you think." Butt beard had drew his rapier against the boy.

"Bring it you codfish!" Finn had pulled his rapier and had charged at the captain. As they had began to clash, it seemed it was at a stalemate. But soon young blueblood was getting more ground on the captain as he was being forced back. noticing this, butt beard had used his demonic stretching powers to stretch a small leg out from his back and used it to kick blueblood's left foot.

"OW! You cheater! I thought we agreed no magic powers!" Blueblood yelled hoping on one foot .

He continued to jump in place for a minute until he had noticed that the pirate captain was aiming to stab him. he had quickly raised his other foot letting himself fall onto the ground avoiding the sword. But he didn't have much time to recover as butt beard quickly brought his rapier down attempting to slice the boy in half.

Blue blood rolled to the side fast enough to avoid a fatal strike. he had quickly got back up on his feet and began trying to poke the captain at least 3 times.

But this did nothing as butt beard had used his mysterious body manipulation powers to avoid all of is strikes.

The first time blueblood targeted his head, but Butt beard had sucked his head into his body avoiding.

The second time he tried hitting one of his livers, but he had stretched his torso far to the left avoiding the second strike.

The third time he tried stabbing the captain in the foot, but he had moved his feet in time and had brought It back around to kick blue blood in the nose.

"Owch! You dirty rat !" Blueblood growled covering his nose.

"Yar har har, how's that feel ya tadpole?!" the captain gloated holding his sides.

But this gave the young pirate an opening. He had returned the favor and had kicked butt beard in the gut with enough force to send him crashing through the door.

"Argh! Me shinbones !" Butt beard yelled as he bounced two times before holding on to a piece of decaying wood on the bridge.

Below him was the bottomless sea, and above him Was Finn blue blood with a smirk on his face.

"Well captain, it seems as someone else has a scheduled trip to Davey jones locker." Blueblood laughed.

"Argh, are ye so cruel that you would send an old man to his watery grave?" Butt beard questioned as he hanged on for dear life on the piece of wood.

"No, I'm not like you, I wouldn't send an old man to his death. Blue blood began clenching his fist.

However, your no old man, you're a murderer and a thief, and you will receive no mercy from me."

Blueblood had drew his rapier and had prepared to slash away at the one piece of the bridge that was supporting the captain .

But just before Blue blood could send the notorious captain to his doom, an eerie hypnotizing sound had filled the air.

"Argh, butt beard, what sort of trickery is this?" blue blood growled as he attempted to cover his ears.

"Is it the sound of the sirens? Oh curse my luck for their song to be the last thing for this man to hear" Butt beard growled as he began losing his grip.

"Oh wait man, I think it's the special occasion phone." Finn said in his normal voice."

It had turned out that the setting was all imaginary. The rapier Finn used was actually a sharpened stick. The clothes he wore were real though.

The so called bottomless sea however was just a small inflatable pool placed conveniently where jake would supposedly land.

There was no rain, just buckets of water falling on them by bmo.

"I wonder who's calling." Jake asked as he turned his body to it's normal form and had stretched down through the front door while Finn went back in the other door.

"SPECIAL OCCASION, SPECIAL OCCASION!" the phone repeated about 3 times before Finn and jake reached it.

"Hello?"

"Finn, there you are! Where were you?!" Peebles questioned frantically

"Whoa, whoa peebels, what's the haps?" Finn asked worried.

"There's no time to explain, just get to the library immediately, we have a serious problem!" Princess bubblegum warned before hanging up the phone.

"What do you think that was about?" Finn turned to his best friend with a look of worry.

But Jake had just shrugged not having any idea.

"Let's just get to the library and find out what's going down, there may be some patoot who needs a good beating." Finn said punching his fist into his palm before running out the door.

"Yeah man, that fool's goanna wish they never messed with us." Jake replied following his bro out the door.

_Meanwhile at ooo's great library, something was amiss. Nurse pound cake and doctor ice cream along with princess bubblegum were circled around one area near the front desk._

"Did you check her pulses?" Bubblegum asked trying to check for a heart beat.

"Yes, there is indeed a pulse but it's faint, and yet it doesn't seem to be changing at all." Doctor ice cream replied as she kept trying to patient to move.

"Oh dear, what a dilemma, who could have done this?" princess bubblegum was worried and distraught at the situation. As she began trying to figure out who could do such a crime, Finn and jake had finally arrived.

"You pebubs, were here, what's the situa…" Finn had cut himself off as most of the people he was feeling and odd tension in the room. He didn't quite understand it, but he knew that this wasn't the time for cheery optimism.

"Dang, what's going on, did something happen?" Jake asked being the first one to speak.

"It's terrible Finn, I don't know who did it, but someone attacked turtle princess. When we got here, this is what we found." Princess bubblegum explained as she stepped back allowing the two heroes to see turtle princess motionless on her back on he dusty library floor.

"Holly…. Turtle princess… is… is she?" Finn stuttered to scared to suggest the word that he was thinking off.

"No, she's not dead… but it doesn't look like she's very alive either, it's a bit hard to explain." Said princess bubblegum looking back at the fallen princess.

But Finn and Jake were at a loss as they had no idea of what she was talking about.

"What are you talking about bubblegum? How can someone be alive but not dead?" Jake questioned.

Bubblegum had sighed not wanting to explain anything further. "Just… come over here for a second." Princess bubblegum motioned them to the none moving turtle.

Finn was the first to notice something wrong. and seeing it was almost enough to scare him.

"H…her eyes… their…" Finn couldn't even finish his sentence. Turtle princess's eyes were open, but something was off about them, they were bleak and void of any describable emotion, it was like she was just a shell of a person now.

(Pun not intended)

Jake had walked over to feel her chest and was shocked. "I.. I can't feel her thumps…" Jake spoke fearfully as he slowly removed his hand from the turtle.

"That's right, I can't locate any thumps on turtle princess… and yet, it seems as though her conscience is still there, but without any thumps to help process that consciousness.. "

"It's as if she's not really there." Finn Finished.

"Do you know what could have happened?" Asked Jake.

"I may have an idea, but I'd never thought I'd live to see something like it." Princess bubblegum had walked over towards a table where a rusty old tome was already opened to a certain page. The page itself had a picture of a heart in someone's hand while an image of a person's eyes were bleak and soulless, much like turtle princess.

"During one of my science expeditions, I had found this old book buried under a dying tree, turtle princess's condition is what I've documented as HKS or Heartless Kairi syndrome.

"Heartless… " Finn began

"Kairi syndrome?" Jake finished.

"Yes, you see long ago there was a war, a war that actually coasted people their hearts, some of the details are a little fuzzy, but one of the people to lose their hearts was a girl named kairi. She lived because her heart was living inside someone, normally, if someone lost a heart, they would have disappeared, but judging how Tp is still alive, I've come to the conclusion that whoever did this to her has her heart and has it resting inside someone or something.

"Wait, so you mean there may be some donk going around stealing people's hearts? That's crazy talk!" Jake yelled.

"I agree, but it's the only possible solution I could come to right now, someone did this to turtle princess, and I need you two to find out who it is."

Princess bubblegum looked back at Finn who was looking at turtle princess with a frightened look on his face.

"Finn, are you ok?" Princess bubblegum asked, worried for the young hero.

"Uh….yeah, stomach's just feeling a little uneasy, so do you have any idea of where the guy could be?"

"I've sent banana guards to go ask the other kingdoms to try to find out what may be happening, but they haven't reported back yet, but whoever did this may be going after the other princesses as well. Get to the other kingdoms and warn the other princess about this threat. I'll try to check in with the banana guards." Bubblegum explained before returning to Turtle princess.

"What? don't you want me to find the guy and smash his face in? what if he reaches the other princesses before I even get there?" Finn questioned not happy about just being a messenger boy.

"We need to think carefully here Finn, not just the candy kingdom is in danger, all off ooo is. But whoever did this managed to pull it off without anyone knowing until it was too late, I must see if there is some way to reason with whoever did this before resorting to force, can you do that for me Finn?" princess bubblegum pleaded looking at Finn with those eyes he fell in love with a long time ago.

Of course it was highly unlikely of it happening due to pb's obsession with work, but that didn't mean Finn didn't have times where he thought about her on a romantic level.

"Y..yes, I'll do it princess." Finn turned away from her still wanting to find the guy who did this and stop him from doing any more harm, but princess bubblegum's reason's were sound, if there was any chance to negotiate with a threat without resorting to force, it would be the first and best option to start with for her and her people.

"Let's go Jake, we need to get to the other princesses before this guy does." Finn said with a look of determination.

Jake had nodded and grew big as Finn jumped on his back and left the library.

_Meanwhile, in the lands between the grasslands and the ice kingdom, the mysterious assassin from the bar was walking alone carrying something in his hand. As the mysterious item continued to sparkle, all he could do was sigh._

"Geez, I thought I was done with getting my hands dirty when I burned that woman's lab to the ground.. of course I guess I can't really cleanse my hands now that I've already put my soul in jeopardy, I wonder if the decision I made was the right one…" Jack continued to mutter as he walked along, but he had just shook his head.

"Eh, what's the point of thinking about the past, all I'll worry about now is getting the job done." Jack spoke as he held a green gem in his hand with a weird aura surrounding it.

**Well, that's the end of the first chapter. first of all a few questions to answer to those who may be wondering what went on in some scenes.**

**First, if you have watched adventure time, you would have probably seen the episode where Finn learned how fun yet dangerous imagination could be, you would have also saw that his imagination land was literally a blank slate when he got there.**

**So for the past weeks or moths I don't really know atm, Jake's been helping Finn learn how to be more imaginative. Sure he's an awesome adventurer, but he was still a kid. And a kid with no imagination is…. Well kind of boring. Of course this is only my opinion.**

**Second, your probably already wondering, how in the world is this suppose to be a crossover Fanfic where Finn meets Fionna if you don't even add them or when are they going to show up or will they show up at all.**

**Well, some people who want to see them crossover to happen already. For those few or bunch, it's called building a story up. in the future chapters Fionna and cake, Marshall lee and etc will appear, but the first half of the story must be completed first before I can make the crossover.**

**I don't know if I'll add characters that have may already been created like Flame prince or not, I may include guys or gals like him if an idea hits me.**

**Thirdly, for those who don't know what the kingdom hearts series is, Go to YouTube and watch a freakin walkthrough, it'll fill in a lot if you couldn't follow some of this story, that is if you have the time.**

**Ok, I've rambled on long enough, leave a review if you plz to tell me your thoughts or suggestions on the story. Also everything except the fanfiction's plot belongs to their respectful owners.**

**With that, I'll see you dude's next chapter.**


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